Democrats have demanded Barr release the entire almost 400-page report and the underlying evidence that Mueller and Barr used to make their conclusions.
Word the Mueller report's release was imminent last week sent President Trump into orbit, declaring during a White House lawn pop-up presser that Mueller's investigation was "illegal", "treasonous" and an attempted coup.
Democrats also are skeptical of Barr's conclusion because he has always been opposed to the special counsel investigation and was hired by Trump.
Barr has been under pressure from Democrats to release the full report without redactions.
The attorney general has pledged to testify publicly about the report's conclusions before the Senate and House judiciary committees - on May 1 and 2, respectively.
Trump and his allies have claimed "total exoneration" in the wake of Barr's letter, but Democrats have said they don't trust Barr to accurately describe Mueller's investigation and have demanded to see the full report and Mueller's underlying evidence.
According to the attorney general's summary, no criminal conspiracy between Moscow and the Trump campaign was established.
The report will detail indictments by Mueller of two Kremlin-backed operations to influence the 2016 election: one against a St Petersburg-based troll farm called the Internet Research Agency accused of waging "information warfare" over social media; and the other charging Russian intelligence officers with hacking into Democratic Party servers and pilfering emails leaked to hurt Democratic candidate Hillary Clinton. Barr said that redactions would be color-coded based on whether they were grand jury information, related to intel sources and methods, information about uncharged parties or information related to ongoing cases.
Barr and his deputy, Rod J. Rosenstein, examined the obstruction evidence laid out by Mueller's team and concluded it did not rise to the level of obstruction of justice.
Attorney General William Barr echoed Trump's insistence last week in congressional testimony that his campaign was spied upon, although he told lawmakers he had so far found no proof. "We don't need you interpreting for us, '" Pelosi said at a recent news conference. Mr Barr concluded that there was insufficient evidence to establish that such an offence had been...